The present invention relates to a heat collector tube and a solar system unit, and more particularly relates to a vacuum glass tube type heat collector tube and a solar system unit including such a heat collector tube or tubes.
Solar system units including vacuum galss tube type heat collector tubes are classified in their mode of use into three significant groups. In the case of the first group, the medium to be heated is continuously supplied to the system and the medium heated by absorption of solar heat is continuously delivered from the system. This group accordingly employs one-way passage of the heat transmitting medium. In the case of the second group, the principle of thermo-syphon mechanism is utilized in which water rises due to its reduced specific gravity resulted from heating by absorption of solar heat. In the case of the third group, the heat transmitting medium is driven for compupulsory circulation through the system unit by a pump.
In the case of the first and second groups, the heat transmitting medium can easily be drained off the heat collector tubes and, consequently, there is no danger of accidental breakage of the heat collector tubes due to freezing of the medium. Since the heat collector tube used for the third group is closed at one end thereof, i.e. at the bottom end, some action needs to be taken in order to prevent breakage of the heat collector tube due to freezing of the heat transmitting medium. For example, the heat collector tubes have to be placed upside down when such freezing of the medium is expected. Despite such a disadvantage, the heat collector tube with a closed bottom end has been increasingly used in practice because of its high efficiency in solar heat collection. In order to meet such increased use of the heat collector tube with the closed bottom end, it is now strongly required to successfully prevent accidental breakage of the heat collector tube due to freezing of the heat transmitting medium.
Further, the vacuum glass tube is very fragile against external shock. In the case of any conventional solar system unit including such vacuum glass tubes, operation of the entire system unit has to be intercepted for replacement of broken heat collector tubes in order to prevent leakage of the heat transmitting medium at the junction of the broken heat collector tube to the system unit.